Increase remote endstop switch/Z probe accuracy

[dc42]

When an endstop switch or Z probe triggers on an expansion board, the board sends a CAN message back to the main board to say that the probe has triggered. This message has high priority but it may be held up for up to about 700us by a low priority message that is already being transmitted. This will affect the accuracy of the trigger position. We could improve accuracy as follows:

1. When the probe or endstop switch changes state, record the system time (local step clock counter converted to master time).
2. When sending the trigger message, include the system time at which the state change was detected.
3. When the master receives the message, stop the relevant drives as now; but then calculate where they would have been at the time that the switch or probe state changed.
4. When sending the revert message to any CAN-connected drivers, tell the drivers to revert to that position.
5. If the axis is driven by any local drivers (either just local drivers or a mixture of local and remote) then we will need to revert the local drivers too.